Impulse generator



Aug. 2, y1949. E. M. osTLUND IMPULS E GENERATOR Patented ug. 2", 1949 UNITED STATES PATENT OFFICE Federal Teken' York, N. Y.,

ne and Radio Corporation, New a corporation of Delaware:

Application February 12, 1945, SerialV N o. 577,439'S (Cl. Z50-G36) 3 Claims. l

This invention relates to radio impulse systems and more particularly to the generation. of impulses for use in pulse modulation systems.

In pulsev modulation systems, particularly where highpower impulses are employed for the modulation of ultra-'high frequency oscillators, it is desirable to obtain frequency stable modulation. Thisis expressed in an improvement of the formfactor of the modulating pulse, that is, an increase in the ratio of the duration of the pulse crest to the build-upy and decay time. Such a condition is of particular' importance in connection with certain types of pulse generatorsemploying spark-gap condenser combinations` which are used to generate short duration, high voltage and high peak power impulses at high repetition rates for employment in pulse modulation inl radio detectiony systems.

- Attempts which have been made in the past to improve the form factor of pulses of this type have generally resulted in appreciable loss of thepeak voltage, a loss of 50% being not uncommon.

It is therefore anobjcct of this invention to providey amethod and meansI for improving the form factor of high voltage impulses.

It is another obiect to provide a method and means for improving the frequency stability in the modulation of a high frequency wave.

It is a further object. to give a flatter top and steeper sides to a highly damped pulse without the loss of the peak voltage thereof.

yIn accordance with my invention, I provide an impulse wave generator which utilizes an openend'ed and substantially non-dissipative delay network such as a lumped or distributed constant line, in shunt with the load which in this instance is an oscillator, or a similar resistive device. The impedance of the loadis equal to that of the network, so that the applied pulse energy is equally divided between the two, that is one-half of the pulse energy is transmitted toward the open end of the line. Upon reiiection from the open end of the llne the pulse, with a delay which is determined by the line constants, ap-V pears as an echo to join the initial half-energy pulse across the load, thereby resulting in a total improved pulse with respect thereto and to be dissipated therein.

The above and other features and objects of this invention will become more apparent upon consideration. of the following detailed description to be read in connection with the accompanying drawings',l in which:

Fig. 1 is a schematic representation of a circuit in accordance with my invention; and Fig. 2

is a graphical illustration circuit of Fig'. 1.

Referring to Fig. I of the drawing, there is shown a modulator lv which is substantially similar to the pulse generator disclosed iny the co'- pending applicatlon'oi" E. Labin-E. NL Ostlund, Seri-al No. 475,733, filed February 13, 1943, Patent No. 2,418,128, dated April 1, 1947, and which comprises three condensers C1, C2, and C3, adapted to be charged in parallel throughY isolating resistors Ri, Ro, Re, R5, and Re, from a rectifier represented by the diode 2. It will, of course. be understood thatl any other suitable type of rectifier means may be. substituted for the diode. The condensers Cr and Cz are connected in series relation by a spark gap Si, the condensers C1 of the operation of the through the load circuit for example, an ultraLhigh so asL to cause the breakdown of the respective spark gaps at a selected point along a cycleof the. applied' alternating the spark gaps are made normally non-conductive for the peak voltage attained by the condensers in response to a cycle of the applied alternati-ng current wave.v These synchronizing voltage pulses for controlling the breakdown ofv the spark gaps may be applied at a suitable time over the input terminals 5 across the resistor R5.

synchronizing voltage impulses may be applied instead, if desired, at other points lnthe circuit to produce the required voltage rise across a given spark gap.

The oscillator 3` may be any known type now used in pulse modulation systems. The only sigiii-'licence of the oscillator in this case is that it generates: anl ultra-high frequency wave and that its effective load impedance modulator l's of a resistive character amounting toa given value such as Zo. In shuntv withV the oscillator 3, there is shown connected a known form of reflecting or delay network 6, which also has an effective impedance of the value Zo, and

current wave, in which case which is comprised of inductance and condensers 8. It will be apparent that the total load impedance presented to the pulses from the modulator I is of the value Zo/ 2.

In the absence of any source of synchronizing pulses for triggering the modulator I, the spark gap Si (the gaps preferably being adjustable) may be adjusted narrower than gaps S2 and S3. This will enable the system to be triggered by the peak potential of the positive one-half cycle of the alternating current applied to the terminals Thus, as the potential of the applied power rises from zero to the positive crest the gap Si will be caused to break down at a selected potential and thereby provide a conductive path. With the first gap conducting, current flows in the adjacent circuit loops so as "to'produce a break down voltage across the second gap Sz. Break down of the two gaps S11 and S2, connects C1, C2 and C3 vin series with the output gap S3 which fires to connect the condensers in series with the load circuitV 3.' A complete discharge of the series break down Vof the condensers thus takes place through the load circuit and the resistance series parallel combinations of the ioslating resistors. The rate of discharge of the series combination of the three condensers is ldetermined by their capacitances and the value of the resistive load Zu. By a proper choice of the values of these discharge parameters, a voltage impulse 9 as shown in graph a of the Fig. 2 is obtainable for application across the load circuit as a source of high voltage energy for pulse modulating purposes. As already indicated above, when a synchronizing pulse is used in connection with the pulse generator, the occurrences of the pulse discharges may be controlled, the spark gaps in that case being adjusted so that they will not be conductive for any voltage value due to the alternating current source alone. The pulse discharge as at 9 in Fig. 2, will be repeated for the instance shown in Fig. 1 with each positive onehalf cycle of the applied alternating current unless the synchronizing pulses applied at 5 cause a controlled predetermined timing different therefrom.

As the pulse discharge 9, which has a peak potential E, is applied across the load circuit, a pulse I0 of only one-half of the energy of the pulse 9 but of substantially the same voltage peak value is impressed vacross the oscillator 3, while an'identical pulse II of i an energy value equal to the other half of pulse 9 is transmitted from the `load 3 toward the open end of the line 6. This division of the pulse energy is, of course, caused'by the fact that two equal impedances are here connected in parallel. However, due to the open end character of the delay or reecting network `I5, the pulse II is here reected and returned to appear across the oscillator 3. This is shown by appropriate arrows in graph b which indicate how the pulse II is reflected back toward the load-where it appears in broken lines as at IIA. The oscillator 3, being of a resistive character, the reflected pulse IIA is here completely dissipated due to the Zu line termination, and accordingly appears as a delayed or echo pulse thereacross which adds with a given time delay tothe initial one-half energy pulse I 0. The delay of the echo pulse IIA referred to as D in graph b, with respect to the occurrence of the pulse I0 is dependent on the line constants of the network 6. If such delay is properly selected, the rlatness of the top of the resulting pulse I2 may be obtained to any required degree. The duration of the pulse I2 for modulating the output of the oscillator 3 in the instance illustrated amounts to approximately 3A of that of the orginal pulse 9. This relation, of course, may be Varied by changing the amount of delay D.

From the above it will be seen that I have provided a method and means for improving the form factor of highly damped pulses without the loss of the original peak voltage thereof.

While I have described the above invention connection with a specic application such as 1n the modulation of an oscillator, and in connection with specic circuits, it will be apparent that the description is by way of illustration only and that the scope thereof is not to be limited thereby except as set forth in the appended claims.

, I claim:

Y1. A Vpulse modulation system, comprising a modulator for producing impulses, a radio frequencyoscillator having a given resistive impedance serving as a Yload for said modulator, and means for improving the form factor of said modulator impulses, comprising an open-ended substantially non-dissipative delay network having an impedance equal to said given impedance arranged in shunt with said oscillator and of an electrical length whereby an initial impulse of a given amplitude transmitted down the network is reflected from the open end thereof and combines with a portion ofthe initial impulse appearing across said load to provide a single improved impulse having said given amplitude.

2. A system for producing modulating pulses comprising means for producing primary pulses, said primary pulse producing means comprising an impulse generator, means for improving the form factor of said primary pulses comprising a load impedance for said generator having a given value comprised of a resistive portion and a substantially non-dissipative portion arranged in parallel therewith, each of said portions having an impedance value which is twice the said load impedance said non-dissipative portion comprising a circuit for delaying an initial impulse applied to said portion in parallel from said generator for a given time period and means for combining saiddelayed impulse with a portion of said initial impulse appearing at the parallel coupling of said two portions to provide a single improved impulse of the same amplitude as said initial impulse'. Y

3. An arrangement according to claim 2, wherein said resistive portion comprises an oscillator circuit to be modulatedby said improved impulse.

EVERT M. OSTLUND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Tonks July 30, 1946 

